1. Technical Field
The present invention relates to processes for producing a polycarbonate which contains constituent units capable of being derived from glucides, e.g., starches, as biomass resources and which has excellent heat resistance, moldability, and mechanical strength and has excellent optical properties including a low refractive index and a large Abbe number. The invention further relates to a polycarbonate obtained by the processes and to molded articles formed from the polycarbonate or a composition thereof.
2. Background Art
In general, polycarbonates are produced from raw materials induced from oil resources. In recent years, however, there is a fear about the depletion of oil resources, and polycarbonates produced from raw materials obtained from biomass resources such as plants are desired to be supplied. In addition, since there also is a fear that global warming caused by an increase in carbon dioxide emission and accumulation thereof may bring about climate changes, there is a desire for the development of a polycarbonate which is produced using a plant-derived monomer as a starting material and is carbon-neutral even when discarded after being used.
A method in which isosorbide is used as a plant-derived monomer to obtain a polycarbonate through transesterification with diphenyl carbonate has hitherto been proposed (see, for example, patent document 1). However, the polycarbonate obtained is brown and unsatisfactory. As a copolycarbonate produced from isosorbide and another dihydroxy compound, a polycarbonate obtained through copolymerization with bisphenol A has been proposed (see, for example, patent document 2). Furthermore, an attempt has been made to improve the stiffness characteristics of the homo-polycarbonate produced from isosorbide, by copolymerizing isosorbide and an aliphatic diol (see, for example, patent document 3).
On the other hand, many proposals have been made on polycarbonates obtained by polymerizing 1,4-cyclohexanedimethanol, which is an alicyclic dihydroxy compound (see, for example, patent documents 4 and 5). However, these polycarbonates have a molecular weight as low as about 4,000 at the most and, hence, many of these have a low glass transition temperature.
As stated above, polycarbonates produced using isosorbide have been proposed. However, no report has been made on a polycarbonate obtained by copolymerizing isosorbide and an alicyclic dihydroxy compound, and optical constants such as refractive index and Abbe number have not been disclosed.    Patent Document 1: British Patent No. 1079686, description    Patent Document 2: JP-A-56-55425    Patent Document 3: International Publication No. 2004/111106, pamphlet    Patent Document 4: JP-A-6-145336    Patent Document 5: JP-B-63-12896